The use of electrically powered projection screens has become quite popular in conference rooms, board rooms and the like. With the touch of a button, the screen may be lowered for use or retracted into its case after use for storage. In some instances, the surface of the case through which the screen extends includes a trap door. When closed, the trap door provides an aesthetically pleasing appearance as the surface through which the screen extends appears to be continuous rather than having a large open slot therein to permit movement of the lower edge of the screen, which usually includes a weight or a dowel across the width of the screen, through the case. Such trap doors also protect the operable components (motor, roller, etc.) which are housed within the case.
In general, trap doors for the cases of electrically powered projections screens are also electrically actuated. The reversible motor used for rolling and unrolling the projection screen or a separate reversible motor is coupled to the trap door such that activation of a motor causes the trap door to move between its open and closed positions. When open, the trap door is pivoted downward away from the interior of the case.
Several improvements to such a trap door system are desirable. First, with regard to the aesthetic appearance of the projection screen case, trap doors of the prior art open away from the case and intrude into the room. Also, these trap doors usually pivot about a hinge located on the exterior of the bottom of the case thereby detracting from the case's appearance when the door is in its closed position. Not only does the exterior hinge of prior art trap doors detract from the aesthetic appearance of the case, the hinge is susceptible to becoming bound or interfered with should the case be painted, for example. Therefore, it is desirable to provide an aesthetically pleasing trap door for a projection screen case which opens into the case to avoid intruding into the room, and to provide a trap door having no exterior hinges to result in a trap door which is flush with the exterior of the case when in its closed position and to avoid the potential problems of the hinge becoming bound or interfered with to hinder the operation of the trap door.
When the trap door of the prior art is in its closed position, one edge of the door is suspended by an exterior hinge and the other edge is only supported by the mechanism connecting the door to its driving motor. Thus, when in its closed position, the trap door may become misaligned or warped. It is therefore desired to provide a trap door which is supported at both of its edges when the door is in its closed position to inhibit potential misalignment or warpage of the trap door.
Some electrically actuated trap doors of the prior art are rigidly affixed to the motor which moves the trap door between its open and closed positions while other electrically actuated trap doors pull the trap door closed and allow the trap door to drop open. In either case, if the driving motor is not functioning properly or if power to the driving motor is unavailable, access to the interior of the case is not possible without disassembling the case. Because projection screen cases are usually assembled using multiple fasteners, disassembly is a time consuming task which results in unwanted delays if the motor driving the trap door is to be replaced or repaired. Further, access to the interior of the case for repair or maintenance of any component therein is essentially denied as the trap door is only open when the screen extends through the case. Therefore, it is desirable to provide an electrically actuated trap door for a projection screen case which allows access to the interior of the case without the provision of power to the trap door's electrically actuating mechanisms.
As previously stated, trap doors of the prior art are essentially rigidly affixed to the door's driving motor for the purpose of closing the trap door, and in some cases for the purposes of opening of the trap door. As a result, when the door moves from its open position to its closed position, the door exerts a great deal of torque. Therefore, in the event an obstruction is placed in the path of the trap door as the trap door moves from its open to its closed position, either the obstruction itself will be damaged or undue stress to the door's driving motor caused by the presence of the obstruction will likely result in damage to the motor. For example, if an individual inadvertently places a finger in the path of the closing door, it is likely that the finger will be pinched or even broken due to the high torque generated by the driving motor. A solid, inflexible obstruction which does not yield to the force exerted thereon by the trap door may, on the other hand, result in damage to the motor or another component of the trap door mechanism. Therefore, it is desirable to provide an electrically actuated trap door which, when closing in the presence of an obstruction in the door's path, does not harm the obstruction or result in damage to the door's driving motor.